Exploring the Lower TertiaryBack-to-back successes at the edge of the deepwater frontier

Since the world’s first modern offshore platforms began appear-ing in the U. S. Gulf of Mexico in thelate 1940s, the petroleum industryhas delivered the energy equiva-lent of more than 40 billion barrelsof oil from the continental shelf, andanother nine billion from the Gulf’sdeepwater basins. Analysts say pro-duction from deepwater wells willlikely eclipse the total productionfrom shallow-water fields in the com-ing decades. One of the most prolificsystems is what geologists call thePaleogene—more often referredto as the Lower Tertiary. Still otherscall it the “final frontier” of deepwa-ter drilling.

Industry’s greatest challenge

Some analysts estimate that the Lower
Tertiary in the Gulf of Mexico holds as
much as 40 billion barrels of oil equivalent (boe). The challenge is that most
of it lies some five miles deep, below as
much as 10,000 feet ( 3,048 meters) of
water and hidden from seismic sensors
by thick layers of salt.

Compared to Miocene plays, mostof the reservoirs found in the LowerTertiary are relatively low permeability.In other words, even though the greatdepth means the reservoir pressuresand temperatures are high, the rock’sability to flow fluids is much lowerthan the Miocene reservoirs. Withoutadditional assistance from improvedcompletions, artificial lift, and possi-bly gas or water injection, oil recoveryrates may be less than 10 percent. Thegood news is that what industry islearning today about the Lower Ter-tiary in the Gulf of Mexico applies toother subsalt deepwater prospects,including those off the coasts of Brazil